A tube fitting assembly has been disclosed in U.S. Pat. No. 3,744,122 wherein a pair of dies inwardly compress a tube onto a tubular part of a fitting. The dies had long and short fingers to alternately overlap to create shear walls and merging walls to promote a good compression inwardly of the tube onto the tubular extension of the fitting. Such tube fitting was contemplated as having both a tube and the tubular extension of the fitting of the same type of metal, for example, aluminum, which could be readily deformed. Such tube fitting did not disclose the use of preformed sharp angled shoulders or biting surfaces on the inner tubular part, and hence was limited in the amount of fluid pressure that it could withstand and the amount of rapid temperature change that it could withstand without leaking.
Another prior art tube fitting was one which used a soft metal sleeve on the outside of a plastic body and the soft metal sleeve was compressed inwardly by a compound movement of three dies so that the plastic body was compressed onto an inner tube. The difficulty with such construction was attempting to insure the uniform compression in all radial directions so that no leakage would occur in the tube fitting. During the compression, first the outer sleeve was made oval in shape and then attempted to be changed to a round cross-section. A major difficulty with this construction was the fact that different tubes have a manufacturing tolerance in dimensions, and if the tube was slightly undersize then the dies had difficulty to compress the sleeves sufficiently for a fluidtight seal.
Another prior art construction was used for sealing a tubular tank onto a nosecone of a rocket. The nosecone had annular ribs to which the tubular tank wall was secured by an inward force which was substantially radially inward in all positions around the periphery. In order to obtain this radially inward force, an explosive impulse was required or a high energy rate magnetic impulse was required. Another alternative was welding. All three such methods could be quite satisfactory for military applications, but for tube fittings manufactured by the millions, the extremely high cost of such seal forming methods made them out of the question from a commercial standpoint.